This study will determine the variability of the frequency and severity of obstructive sleep apnea syndrome (OSAS) in children. We hypothesized that the overnight polysomnogram provides a reproducible measure of sleep-disordered breathing in children. Otherwise normal children who presented to the outpatient clinic with symptoms of sleep-disordered breathing sufficiently severe to clinically warrant an overnight polysomnogram were asked to participate. Subjects underwent two polysomnograms performed no more than 4 weeks apart. The investigators were blinded as to the scoring and interpretation of the polysomnograms. The variability measured will be a composite of the physiologic variability within individuals, the polsomnographic signal-quality variability, and the polysomnographic scoring variability. Data from this study will help to better characterize respiratory disturbance during sleep in children and are critical to the interpretation of future studies examining the natural history of OSAS and the efficacy treatment.